(1) Field of the Invention
The present invention relates to a process for preparing a cinnamate ester. The process comprises reacting a styrene compound having a structure that corresponds to the structure of the cinnamate ester to be prepared with an alcohol, carbon monoxide and oxygen in the presence of a catalyst. The heat evolved during the reaction is readily removed from the reactor, thus providing an economical and industrially practical process for preparing a cinnamate ester.
(2) Description of the Related Art
Cinnamate esters are useful as perfume bases and as starting materials therefor. They are also important as starting materials for agricultural chemicals, photosensitive resins and in the synthesis of the amino acid phenylalanine.
Cinnamic acid has conventionally been produced by a process in which benzaldehyde and an acetic acid derivative are used as the principal starting materials. However, such starting materials are expensive and thus, the cinnamic acid produced is also expensive. Accordingly, such a process is not economical for use on an industrial scale.
A process for making a cinnamate ester from less expensive starting materials has been proposed wherein a styrene compound is reacted with carbon monoxide, an alcohol compound and oxygen in the presence of a catalyst. (See Japanese Patent Application Laid-Open Nos. 15242/1981, 70836/1982, 92242/1985 and 77352/1987 and U.S. Pat. No. 4,661,620). However, the proposed reaction is oxidative and releases a large amount of heat. Thus, for industrial use, an effective method for removing the heat is needed. Prior art reactions for preparing a cinnamate ester relate to only small scale production. The prior art does not suggest an effective method for removing the large heat of reaction produced when the process is practiced on an industrial scale.
In a general reaction, it is routine to use a jacket cooler provided outside a reactor or a cooling tube disposed in a reaction mixture to remove heat evolved in the reactor. However, such methods are limited to reactions practiced on a small scale or to reactions of an extremely small heat release value. Where a large amount of heat is evolved in the present reaction (for example, the heat of reaction from styrene to methyl cinnamate is about 81 kcal/mole) use of the above routine methods fails to provide a sufficient heat transfer area commensurate with the exotherm rate for practicing the process on an industrial scale. Thus, none of these methods can be used industrially as the principal method for removing the heat of reaction. However, such methods may be used as auxiliary heat removal methods.
One skilled in the art may contemplate circulating the reaction mixture through an external heat exchanger. However, such method poses the problem that complex facilities are required, as well as additional energy to circulate a large amount of liquid.
On the other hand, another method for removing heat uses the heat of evaporation of a liquid component in a reactor. However, the method is generally employed under conditions wherein a solvent boils, and thus is not effective when a reaction is carried out below the boiling point of the solvent.